These are brief descriptions of realistic scenarios involving the impact of a typical stony meteor/asteroid of various sizes. The diameter in meters or kilometers is given, as well as a statement regarding the atmosphere's effect upon the asteroid, followed by a brief description of the event and several sentences describing the consequences. You might be amazed at the magnitude of the destruction by something so small, but this is tied to the fact that the impact velocities vary from 10 km/s to 72 km/s (22,000 mph to 160,000 mph)!

0.1 m: fireball, with deceleration to terminal velocity


A meteorite the size of a large grapefruit smashed through the roof of a suburban high school outside of Paris today, striking a science teacher on the hip and causing massive bruises over the lower part of his body. Students working on astronomy projects in the same room were unharmed. This is only the second instance in recorded history of a person being struck by a meteorite. Scientists who rushed to examine the stony meteorite said that it undoubtedly originated on the surface of Mars. Microscopic examination of the meteorite may provide new evidence in the ongoing controversy over the possibility of life on the red planet.
 

3 m: fireball, with deceleration to terminal velocity


METEORITE LANDS NEAR FISHERMAN'S WHARF; CRUSHES MIME.

At 5:00 PM this afternoon, a enormous fireball was observed over the west coast of the United States. The fireball appeared to break apart in mid-air over San Francisco. Seconds later, an iron meteorite weighing nearly a hundred tons crashed into the front of a T-shirt store near San Francisco's famed Fisherman's Wharf, crushing a mime in the middle of a performance and creating a hole nearly ten feet deep. It is the largest such meteorite ever seen, surpassing the 34-ton Ahnighito meteorite discovered in Greenland, and the 66-ton Hoba meteorite of Africa.

Although native San Franciscans seemed unimpressed, a crowd of tourists immediately gathered around the meteorite, and discovered to their surprise that it was cool to the touch. Speculating about why such a massive object had not made a larger hole, a prominent scientist theorized that it had entered the Earth's atmosphere at a very low angle, allowing its speed to be slowed by atmospheric friction.

Rush-hour traffic jams in central San Francisco were observed to be unusually severe in the aftermath of the fall.
 

50 m: airburst after sudden shock at the troposphere


2:00 PM Tuesday: A giant meteorite exploded in the atmosphere six miles above San Francisco today, creating a shock wave which is estimated to have destroyed every building within a five-mile radius. The heat from the blast ignited a firestorm which incinerated most of San Francisco, causing thousands of deaths. Cars were overturned and windows shattered as far away as Sacramento.

In spite of worldwide asteroid-detection efforts in recent years, astronomers had no warning of the incoming meteorite, which was too small to be picked up by the most advanced telescopes until  moments before it hit.

As appalling as the damage was, scientists say we were lucky. This one was a stony meteorite. If it had been made of iron, like the one which created the Barringer Crater in Arizona, it would have vaporized San Francisco and devastated most of northern California.
 

700 m: land impact, with little deceleration


At approximately 8:15 this evening, Asteroid 2004 Cyrus struck the Earth 5 km west of Paris, France. Since the discovery of its trajectory and impending impact about six months ago, the governments of Western Europe have done their best to relocate the populations of France, Belgium, Luxembourg and the Netherlands.The force of the impact, equal to that of 50,000,000,000 tons of TNT, annihilated the city of Paris in an instant. The shock wave from the explosion flattened large areas of London, Brussels, Antwerp andAmsterdam, while the intense heat ignited firestorms across much of France. The cloud of smoke and dust from the explosion and fires is expected to alter the climate of the Earth for a period of months or years, causing crop failures and possible mass starvation.
 

700 m: ocean impact, with little deceleration


At approximately 11.45 this morning GMT (night time in Japan) a meteorite landed 500 miles south of Tokyo in the Pacific Ocean. Giant tsunamis have destroyed all coastal and island areas for thousands of miles. Damage is devastating for the islands of Japan, the Korean peninsula and much of Northern China. Death tolls are expected to reach as high as 100 million. Specific damage reports are as of yet unavailable.
 

1.7 km: land impact, with virtually no deceleration


At approximately 4:27 this morning EDT Asteroid 2004 Cyrus landed on New York City. Since the discovery of its trajectory and impending impact about one year ago the governments of the US and Canada have done their best to relocate the populations of areas within 500 miles of New York City. With the force of its blast estimated at 1,000,000,000,000 tons of TNT, the shockwave flattened buildings over much of New England and the Mid-Atlantic states. Firestorms are raging across the eastern United States as far as the Mississippi, creating a cloud of smoke and dust
which will create life-threatening weather conditions worldwide. Predictions are for global cooling on the order of 4-8 degrees celsius (8-20 degrees Fahrenheit). Massive crop failures may lead to global starvation and hundreds of millions of additional deaths.
 

1.7 km: ocean impact, with virtually no deceleration


At approximately 10.15 this morning GMT (night time in Japan) a meteorite landed 500 miles south of Tokyo in the Pacific Ocean. Giant tsunamis full of churning debris have destroyed all coastal and island areas for hundreds of thousands of square miles. All of Japan and the Korean peninsula, along with much of China, the Philippines and Indonesia have been totally destroyed, with the loss of over a billion lives.

At this moment, 300-foot high tsunamis are heading for the Pacific coasts of North and South America. Chaos is reported as millions of terrified people attempt to flee the advancing  wall of water, which may sweep inland as much as a hundred miles. The long-term environmental consequences of the impact are as yet unpredictable, but are likely to be devastating.
 


It should be noted that currently we cannot detect ANY asteroids of these sizes unless they pass within distances corresponding to a few Earth-Moon distances. A reasonably good census of asteroidal objects exists for diameters exceeding 12 km or so, depending upon the reflectivity (and so composition) of the asteroid. This situation should change for the better in the near future. Anything that large hitting the Earth, however, would devastate most forms of advanced life. Luckily, most of the orbiting debris out there is very small, usually vaporizing in our atmosphere to give us a harmless shooting star display. But while the chances of one of these larger objects hitting the Earth are slim, they are not zero, and the consequences are enormous. Any risk analysis takes into account probability of occurence as well as the impact (no pun intended) of a positive result. These scenarios, and others, can be found at this web site.